KR840001593B1 - Process for the purification of p-aminophenol - Google Patents

Abstract

Recovery and extractive purifice. of p-aminephenol (I), obtd. by catalytic reduction of PbNO2 in an aq. acid medium (with 4,4'-diaminodiphenyl ether (II) and aniline present as impurities), involves adjusting the feed soln. to PH 4-5 with base. Then, the solution is extracted with a mixture of aniline and toluene (4:1-1:4) to exract (II) selectively and to leave an aq. phase from which (I) is recovered. The procedure is more selective in removing (II) than prior procedures, and (I) of improved purity is obtd. in greater overall yields. (I) is used in the prepn. of the analgesic acetaminophen and so high purity and esp. low (II) content is desirable It is also useful in the prodn. of dyestuffs and photographic chemials.

Description

Method for Purifying Para-Amino Phenol

The present invention relates to a method for purifying para-aminophenol, particularly a method for recovery and extraction and purification of para-aminophenol which selectively removes 4,4'-diaminophenyl ether which is a main impurity.

Para-aminophenol (PAP) is a well known major intermediate used in the preparation of the analgesic acetaminophen (APAP) and is also used as an intermediate in the manufacture of dyes and photographic chemicals. It is preferred that para-aminophenol is particularly high when used in the preparation of acetaminophen, i.e. free of 4,4'-diaminodiphenyl ether.

An important commercially widely used method of preparing PAP is to hydrogenate nitrobenzene in the presence of a catalyst in a strong acid medium. In this basic process, the hydrogenation of nitrobenzene is carried out using a platinum / carbon catalyst in the presence of 10-13% sulfuric acid solution containing a small amount of surfactant such as dodecyltrimethylammonium chloride. This reaction is rather complicated and by this reaction a large amount of aniline and various small amounts of amines [4,4′-dinodiphenylether (aka oxydianiline or ODA), ortho-aminophenol, para Including affinodiphenylamine and para-hydroxy difinylamine. These byproducts, which are potent impurities in the PAP end product, can generally be dissolved in an acidic aqueous medium. 4,4′-diaminodiphenyl ether is a small amount of amine which is a major component of the by-product and when PAP is used in the preparation of pharmaceutical compounds, it should be present in the pharmaceutical compound of less than 20 ppm, preferably less than 10 ppm.

In a particularly advantageous method of preparing PAP by hydrogenation of nitrobenzene in the presence of a catalyst in aqueous sulfuric acid, the hydrogenation reaction is interrupted before the nitrobenzene injected into the reaction vessel is exhausted. See US Patent No. 3,383,416 to Benner. (1968.5.14)] The catalyst is susceptible to suspension in the nitrobenzene layer and is easily separated by decanting an aqueous reaction mixture containing PAP, aniline and small amounts of amine by-products in salt form.

As mentioned above, preferably the PAP used to prepare the APAP should be very pure, in particular free of 4,4'-diamino diphenylethers. In advanced terms of para-aminophenol, the purification method is described in the patent literature. In addition to Benner's US Patent No. 3,383,416, the following patent relates to a process for preparing para-amino phenols:

United States Patent No. 3,658,905, British Patent No. 1,028,078

United States Patent No. 3,694,508 and British Patent No. 1,038,005

United States Patent No. 3,703,598, British Patent No. 1,228,568

United States Patent No. 3,717,680, British Patent No. 1,291,642

United States Patent No. 3,845,129, British Patent No. 1,516,380

U.S. Patent No. 3,876,703,

U.S. Patent No. 3,917,695,

U.S. Patent No. 4,139,562,

U.S. Patent No. 4,176,138, and Japanese Patent Application No. 54 (1979) -73741.

In US Pat. No. 3,717,680 to Byron et al., Aniline is added to the aqueous reaction product produced by the basic bener method and the pH is increased to 6.0 or greater, preferably 6.5 to 7.5 (at this pH PAP is in the form of a free amine). The solution is then cooled and the PAP is crystallized, filtered and washed first with aniline, then with toluene, then separating the aniline phase containing 4,4'-diaminodiphenylether and other small amounts of amine by-products from the aqueous phase. .

Japanese Patent No. 54 (1979) -73741 discloses the purification of a purified para-aminophenol obtained by partially neutralizing the catalytic reduction reaction mixture resulting from the catalytic reduction of nitrobenzene with alkali to pH 3.5-5. The manufacturing method is described. Aromatic amines such as aniline are added and the 4,4'-diaminodiphenylether and other sulfate-bound impurities in the aqueous phase are optionally substituted with aromatic amines. The liberated impurities are extracted with excess aromatic amine and removed. The recovered aromatic amine phase is washed with alkaline aqueous solution and recycled to use for partial neutralization of the catalytic reduction reaction mixture.

U.S. Patent No. 3,845,129 to Ryde describes a process for the recovery of para-aminophenol in purified form prepared by catalytic reduction of nitrobenzene, wherein anilinepa 4,4′-diaminodi Phenyl is present as an impurity and the method is as follows: pH4.8 to 5.5, in particular 5.0 to 5.5 (at this pH, para-aminophenol is precipitated and aniline and 4,4'-diaminodiphenylether are in freebase form). The solution of para-aminophenol and impurities in the aqueous medium of the present invention is intermittently contacted with an extraction medium consisting of a water immiscible, mainly non-oxidized solvent (e.g. methylene chloride, chloroform, carbon tetrachloride, etc.). This solvent dissolves the impurities and recovers the purified para-aminophenol from the aqueous phase. Toluene is a relatively unsuitable solvent for 4,4'-diaminodiphenyl ether.

Yamamoto's U.S. Patent No. 4,139,562 discloses a crude para-aminophenol prepared by catalytic reduction of nitrobenzene in an aqueous sulfuric acid medium with alkali in the presence of a reducing agent such as sodium dithionite or sodium sulfite in an inert gas atmosphere such as nitrogen. The pH is adjusted to between 7 and 8 and the resulting precipitate of crude para-aminophenol is separated from the liquid phase. Next, the separated para-amino phenol is dissolved in an aqueous alkali metal solution to form an aqueous alkali metal salt solution of the crude para-amino phenol, which is then contacted with a water-immiscible inert organic solvent to selectively extract impurities present in the system from the organic solvent. Be sure to Preferred organic solvents are aniline.

Satte U.S. Patent No. 4,176,138 describes a process for preparing para-aminophenol by catalytic hydrogenation of nitrobenzene in an acidic reaction medium, in which dimethyldodecylamine sulfate is substituted for trimethyldodecyl ammonium chloride. Substitution removes specific impurities.

In US Pat. No. 3,876,703 to Hermett et al., A crude para-aminophenol comprising preparing a mixture of crude para-aminophenol aqueous solution nitrobenzene and adjusting the pH of the mixture to 4.5 to 7.5 and then separating the nitrobene phase The purification method of is described.

These purification methods and other methods described in the above-mentioned patent documents are of some utility, but are more selective in removing 4,4′-diaminodiphenyl ether from PAP, with higher total yields. There is a need for a purification method that provides PAP with improved purity and is capable of preventing inherent PAP loss in the prior art methods.

It is an object of the present invention to provide improved recovery and extraction for para-aminophenols that produce para-aminophenols containing 4,4'-diaminodiphenyl ethers at low concentrations, preferably below 20 ppm or below 10 ppm. To provide a way. Another object of the present invention is to improve the purification of para-amino phenols with less total loss of para-aminophenols by maximizing the removal of 4,4′-diaminodiphenyl ethers and minimizing the loss of para-amino phenols. To provide a way.

In the process for the recovery and extraction of para-aminophenols prepared by the catalytic reduction of nitrobenzene in the acid medium according to the invention, where 4,4′-diaminodiphenyl ether and aniline are present as impurities, para Aqueous feed solution containing 4,4′-diaminodiphenylether and aniline present as aminophenol and impurities was neutralized with base to adjust the pH of the solution to 4.0 to 5.0, and the resulting raw aqueous solution Was extracted with an organic solvent composed of a mixture of aniline and toluene in a ratio of 4 vol. 1 vol. To 1 vol.: 4 vol. To 4,4′-diamino diphenyl ether. By selective extraction with a solvent, an organic phase containing primarily an aqueous phase containing para-aminophenol and para-aminophenol, 4,4′-diaminodiphenyl ether and other small amounts of amine by-products It is characterized by forming an aniline-toluene phase, separating the aqueous phase from the aforementioned organic phase and recovering the increased purity of para-aminophenol from the aforementioned aqueous phase.

Preferably, the organic phase containing aniline, para-aminophenyl and 4,4'-diaminodiphenyl ether is back extracted with a basic solution of potassium hydroxide or sodium hydroxide to recover the para- originally contained in the basic solution and the organic phase. An aqueous layer containing almost all of the aminophenol and a residual organic phase containing almost all of the 4,4′-diaminodiphenyl ether originally contained in the organic phase were obtained and this aqueous layer was recycled and used as part of the base to Adjust the pH of the raw aqueous solution to 4.0 to 5.0. This method can be carried out using conventional apparatus.

The organic phase can be back extracted using an ammonium sulfate solution having a pH of about 4.8 to 5.0 in place of potassium or sodium hydroxide. In another aspect of the present invention, the advantages of preparing higher purity para-aminophenol and improving yield are as follows. That is, 4,4 by fractional counter current extraction of para-aminophenol and a raw material solution containing the above-mentioned impurities and having a pH of about 4.0 to 5.0 with an aniline-toluene mixture and ammonium sulfate solution, aniline sulfate or sulfuric acid 4,4 '-Diaminodiphenyl ether is optionally extracted with aniline-toluene mixture to contain an aqueous phase containing primarily para-amino phenol and para-aminophenol, 4,4'-diaminodiphenyl ether and other byproduct amines The organic aniline phase is obtained and then the aqueous phase is separated from the organic phase and the para-aminophenol with improved purity is recovered from the aforementioned aqueous phase.

Using the present invention, para-aminophenols having increased purity can be prepared by recovery and extraction purification, wherein aniline as para-aminophenol and impurities, prepared by catalytic reduction of nitrobenzene in an acidic medium. And a raw material aqueous solution containing 4,4′-diaminodiphenyl ether is first reacted with a base to adjust the pH of the raw material aqueous solution to about 4.0 to 5.0 and then extracted with an organic solvent consisting of a mixture of aniline and toluene. Under certain pH conditions and organic solvents, major impurities, i.e., 4,4'-diaminodiphenyl ethers, are more selectively extracted into the organic solvents to improve purity, resulting in improved purity of para-aminophenols, i.e. 4,4'-diaminophenyls. It is possible to obtain para-aminophenol having an ether content of less than 20 ppm, more preferably less than 10 ppm, as in the examples described below.

As mentioned above, the starting materials used in the present invention are para-aminophenol, aniline, 4,4'-diaminodiphenyl ether and other small amounts, produced by the catalytic reduction in sulfuric acid medium of nitrobenzene. Aqueous aqueous solution containing amine by-products [US Patent No. 3,383,416 to Benner] The aqueous solution of the raw material may also contain a small amount of unreacted nitrobenzene or be treated to remove almost all nitrobenzene before carrying out the invention. have.

The aqueous solution of the raw material is first reacted with a base to adjust the pH of the solution to about 4.0 to 5.0. This is an important point of the present invention because in this pH range 4,4′-diaminodiphenylether, aniline and small amounts of amine byproducts (which are weaker bases than para-amino phenol) are liberated in the form of freeamine, This is because aminophenols exist mainly in the form of sulfates. Thus, due to the difference in basicity of these compounds, the unwanted components are present in the form of free amines and the desired components are present in the form of sulfates of para-aminophenols.

As can be seen from the experimental results described below, the pH in the range of 4.0 to 4.5 is very advantageous for the para-aminophenol to be retained in the aqueous phase while the pH in the range of 4.5 to 5.0 removes 4,4'-diaminodiphenyl ether. Very advantageous to do. However, both objects within the scope of the present invention can be achieved by using a sufficient number of extraction steps in the entire pH range of 4.0 to 5.0.

Particular preference is given to using a base such as ammonia (including ammonium hydroxide) or potassium hydroxide in order to adjust the pH of the starting aqueous solution to 4.0 to 5.0. However, any alkali metal hydroxide or alkali metal salt of para-aminophenol can be used for this purpose. In addition, the pH of the raw material aqueous solution can be adjusted to 4.0 to 5.0 using a base solution containing sodium hydroxide or potassium hydroxide and a part of the base used by recycling the para-aminophenol produced in the reverse extraction step described later.

After quenching to the desired pH, the raw aqueous solution is extracted with a mixture of aniline and toluene to selectively dissolve 4,4′-diamidiphenylether and mainly to an aqueous phase or paraimate containing para-aminophenol and to extract para and An organoaniline-toluene phase is produced which contains almost all of the 4,4'-diaminodiphenyl ether originally contained in the aminophenol, the aqueous solution of the raw material and other aniline-toluene soluble impurities. According to the present invention, preferred results are achieved when the ratio of aniline: toluene is between about 4: 1 (volume parts) and about 1: 4 (volume parts). In order to remove the same amount of 4,4'-diaminodiphenyl ether while reducing the PAP dissolution loss rate in the organic solvent, it is preferable to use the ratio of aniline: toluene at 1: 1 (volume portion). In this organic solvent mixture, aniline acts as an extractant while toluene acts as an anti-solvent and diluent. Thus toluene is a poor solvent for para-aminophenol and 4,4'-diamino diphenyl ether, but when mixed with aniline in such proportions, the resulting mixture has the desired solvent and desirable physical properties.

Extraction of 4,4'-diaminodiphenyl ether from the starting aqueous solution may be carried out in a discontinuous or continuous process. This extraction is preferably carried out on a countercurrent extraction column, such as a car reciprocating plate countercurrent extraction column, or other similar column known in the art. It is also possible to use devices such as centrifugal reflux extractors, pump-decanters, vibratory columns or mixed-precipitators. Thus, for example, when using a countercurrent column, the content of 4,4'-diaminodiphenyl in the aqueous phase of para-amino phenol is obtained by using a 50% -50% aniline-toluene mixture at pH 4.8 in three to four steps. Theoretical extraction step can reduce to less than 50ppm, typically less than 10ppm, while using aniline alone can contain 4,4'-diodinodiphenylether at the same low concentration at a given organic relative aqueous phase. In order to do this, a five-stage extraction requires 16 to 20 cross-flow extractions using only aniline in a discontinuous process.

In addition, the volume ratio of aniline-toluene to raw material aqueous solution is an important factor in performing the extraction step. In general, lower ratios are preferred because less para-aminophenol is extracted to the organic phase, so that more para-aminophenol can be present in the aqueous phase. The volume ratio of the aqueous solution of aniline-toluene raw material is 0.05 to 1: 1, preferably 0.2: 1.

Once the extraction is complete, the aqueous phase or extraction mainly contains most of the para-aminophenol with some aniline and a very small amount (less than 50 ppm based on para-aminophenol) of 4,4'-di-aminodiphenylether The debris is separated from the organic phase. Ammonium hydroxide is then added to the aqueous extract, which is an aqueous phase, and neutralized to pH 7-8 to precipitate the partially purified para-aminophenol product. Precipitation of para-aminophenol occurs at pH 5-8, but since the minimum solubility of para-aminophenol is pH 7-8, most products precipitate within this pH range.

The precipitated para-aminophenol is then collected by filtration, washed with toluene and sodium bisulfite solution and dried in vacuo. Toluene removes all attached aniline and sodium bisulfite acts as an antioxidant. The anhydrous para-aminophenol product thus obtained typically contains less than 10 ppm 4,4'-diaminodiphenylether and has an acceptable purity for acetaminophen preparation.

The organic phase or organic extract containing the aniline, para-aminophenol and 4,4′-diaminodiphenylether, which has undergone the extraction step, is distilled to recover aniline for reuse or to recover additional para-aminophenol. Further treatment as described below can be done to improve the overall yield of para-aminophenol.

Therefore, the aqueous layer and the organic phase preferably containing almost all of potassium hydroxide or sodium hydroxide and para-aminophenol originally contained in the organic phase by preferably back-extracting the organic phase by adding sodium hydroxide or potassium hydroxide solution, preferably potassium hydroxide, to the organic phase. The remaining organic phase containing almost all of the 4,4'-diaminodiphenyl ether originally contained in is produced. The concentration of potassium hydroxide or sodium hydroxide solution should be above the concentration necessary to convert para-aminophenol to its phenolate salt form. In general, for example, the concentration of potassium hydroxide should be 10 to 50% by weight.

The pH of the aqueous layer obtained from back extraction is at least 12. The pH of this aqueous layer can be adjusted to 7 to 8 by adding concentrated sulfuric acid to precipitate solids containing industrial grade para-aminophenol. According to the present invention, however, the aqueous layer is recycled and used as part of the base used to adjust the pH of the original raw aqueous solution to 4.0 to 5.0, thereby reintroducing para-aminophenols which are not recovered from the aqueous phase into the main reaction oil. It is extremely desirable to further increase the filling rate of the improved purity of the para-aminophenol through the basic extraction reaction described above.

Aniline and toluene can be recovered and reused from the residual organic phase by distillation.

Instead of back extracting the organic phase resulting from the basic extraction step with a solution of potassium or sodium hydroxide, back extraction of the organic phase with an ammonium sulfate solution further increases the total yield of para-aminophenol.

However, according to another aspect of the present invention, car reciprocal extraction of a raw aqueous solution containing para-aminophenol, aniline, 4,4′-diaminodiphenyl ether and other small amounts of amine by-products and having a pH of 4.0 to 5.0 It is desirable that the yield of para-aminophenol with improved purity can be increased by fractional extraction with a mixture of aniline and toluene and ammonium sulfate solution, aniline sulfate or sulfuric acid at pH 4.8 to 5.0, as in the column. To do this, a 15% ammonium sulfate solution at pH4.8 to 5.0 or a 1.5% ammonium sulfate solution at pH 4.0 can be used. Instead of ammonium sulfate, aniline sulfate or sulfuric acid may be used. When sulfuric acid is used, aniline sulfate is formed together with aniline present in the organic phase. 4,4'-diaminodiphenyl ether is again optionally extracted with aniline-toluene mixture. Extraction as described above results in an aqueous phase containing more para-aminophenol present in the aqueous solution of the raw material than in the aforementioned extraction step using the aniline-toluene mixture without using ammonium sulfate solution for back extraction of para-aminophenol. Is generated. The organic phase thus produced contains almost all of the 4,4'-diaminodiphenyl ether previously contained in the raw aqueous solution. The aqueous phase containing para-aminophenol is separated from the organic phase and treated as described above to give an improved purity of para-aminophenol containing less than 10 ppm 4,4'-diaminodiphenylether. The organic phase can be used for aniline-toluene recovery and further para-aminophenol recovery as described above.

The following examples illustrate the invention.

Example 1

P-amino obtained by catalytic hydrogenation of nitrobenzene in sulfuric acid solution containing a small amount of dodecyltrimethylammonium chloride in the presence of a p _t / c catalyst (US Pat. Phenol hydrogenated solution (10 l) is added to a 12 l round bottom flask and ammonium hydroxide (1 l) is added to adjust the pH to 4.8 to 5.0. Alternatively, an aqueous phase containing potassium hydroxide and p-aminophenol (obtained as described in Example 2) may be used instead of a portion of ammonium hydroxide. Aqueous p-aminophenol solution prepared at pH 4.8 to 5.0 contains 100 mg / ml of p-aminophenol (sulfate salt form), 20 mg / ml of aniline and 3 mg / ml of 4,4'-diaminodiphenyl ether as main components. It is contained. The solution was heated to 85 to 90 ° C. using a heating mantle and a heat insulated meteing pump at a rate of 250 ml / min to the top of the Carrec plate extraction column with a 1 ″ diameter, 8 ′ height plate attached to the plate. To supply. At the same time, 50 vol% -50 vol% aniline and toluene mixtures (1.1 l) were fed to the base of the column at a rate of 50 ml / min at 85 ° C. through a similar reforming pump at 85 ° C. to obtain the desired backflow flow pattern of the droplet dispersion and coalescence of the extraction column. Established by normal operation. After reaching equilibrium, the aqueous extractor phase contains about 90 mg / ml of p-aminophenol, 35 mg / ml of aniline and less than 0.001 mg / ml of 4,4'-diaminodiphenyl ether. The organic or aniline-toluene extract phase also contains about 50 mg / ml of p-aminophenol, 15 mg / ml of 4,4'-diamino diphenylether and other aniline-toluene soluble impurities. The aqueous extract residue (11l) was collected and neutralized with ammonium hydroxide to adjust the pH to 7.0-8.0 to precipitate the partially purified p-aminophenol product. The product was collected by filtration, washed with toluene (750 ml) and 10% sodium sulfite solution (300 ml) and dried in vacuo to give 950 g of anhydrous p-aminophenol containing up to 10 ppm of 4,4′-diaminodiphenylether. To obtain. The organic extract is useful for recovering aniline by distillation or for recovering p-aminophenol as in Example 2 described later.

Example 2

Example 1 was repeated but the resulting hot organic extract phase (about 2.2 l) was separated and placed in a 5 l round bottom flask equipped with a stirrer and the organic phase cooled to ambient temperature. An aqueous sodium hydroxide solution (90 ml, 10% by weight) is added to the organic extract, the heterogeneous mixture is stirred for 15 minutes, then left to stand for 5 minutes and the layer is decanted and separated. This aqueous layer contains 1.5% of the 4,4'-diaminodiphenyl ethers contained in the original organic phase of 97% of the p-amino phenol contained in the original organic phase and 3% of p-aminophenol in the remaining organic phase. And 98% of 4,4'-diaminodiphenyl ether. This aqueous phase can be mixed with ammonia or other bases as described in Example 1 for use in the initial neutralization step (to adjust the pH of the aqueous phase to 4.0 to 5.0) or separated to recover p-aminophenol. Can be used. Concentrated sulfuric acid is added to the aqueous phase (about 900 ml) while cooling to precipitate a solid containing 154 g of industrial p-aminophenol.

Example 3

Repeat Example 1 but adjust the pH of the aqueous phase to 4.5 by adding ammonium hydroxide. Aqueous extract residue pairs produced after equilibrium contain 97 mg / ml of p-aminophenol, 35 mg / ml of aniline and less than 0.001 mg / ml of 4,4'-diamino diphenyl ether. The extract phase contains about 16 mg / m of p-aminophenol, 15 mg / ml of 4,4'-diamino diphenyl ether and a small amount of other impurities.

Example 4

Repeat Example 1 but adjust the pH of the aqueous phase to 4.0 by adding ammonium hydroxide. Aqueous extract residues generated after equilibrium contain 98 mg / ml of p-aminophenol, 35 mg / ml of aniline and less than 0.001 mg / ml of 4,4'-diaminodiphenyl ether. The phase contains about 12 mg / ml of p-aminophenol, 15 mg / ml of 4,4'-diaminodiphenyl ether and a small amount of other impurities.

Example 5

Example 1 is repeated but 25% to 75% (vol%) of aniline and toluene mixtures are used as organic solvent. The aqueous extractive phase produced after reaching equilibrium contains 94 mg / ml of p-aminophenol, 35 mg / ml of aniline and 0.015 mg / ml of 4,4′-diaminodiphenyl ether. It contains about 30 mg / ml of p-aminophenol and 15 mg / ml of 4,4'-diaminodiphenyl ether.

Example 6

Example 1 is repeated except that 75% -25% (volumes) of arinyl and toluene mixtures are used as organic solvent. The aqueous extract residue formed after reaching the parallel state contains 88 mg / ml of p-aminophenol, 33 mg / ml of aniline, and less than 0.001 mg / ml of 4,4′-diaminodiphenyl ether. The phase contains 60 mg / ml of p-aminophenol and 15 mg / ml of 4,4'-diaminodiphenyl ether.

Example 7

Example 1 was repeated but the p-amino phenol hydrogenation solution and aniline-toluene were prepared in the same manner for the carreflow extraction column and the pH of the p-aminophenol hydrogenation solution was adjusted to pH 4.8 to 5.0 in the same manner. In addition, sulfuric acid was added to prepare 1 l of a 1.5% ammonium sulfate solution at pH 4.0. The p-aminophenol hydrogenated solution is fed at the rate of 250 ml / min to the center of the car column at 85 ° C. and aniline-toluene and ammonium sulfate are fed at the rate of 50 ml / min to the base and top of the column at 85 ° C., respectively. The column is operated to obtain a clear phase separation at half the bottom of the column in four theoretical steps. After reaching equilibrium, the aqueous extract residue contains about 99 mg / ml of p-aminophenol, 35 mg / ml of aniline and less than 0.001 mg / ml of 4,4'-diaminodiphenyl ether. It contains about 5 mg / ml of p-aminophenol, 15 mg / ml of 4,4'-diaminophenol ether and other aniline-toluene soluble impurities. The aqueous extract residue was collected and treated as in Example 1 to give 990 g of anhydrous p-aminophenol containing 4 ppm or less of 4,4'-diaminodiphenyl ether.

Example 8

Repeat Example 7 but use aniline sulfate solution prepared by titrating 2% sulfuric acid to pH 3.8 with aniline in place of 1.5% ammonium sulfate solution. After reaching equilibrium, the aqueous extract residue contains about 99.0 mg / ml of p-aminophenol, 45 mg / ml of aniline, and less than 0.001 mg / ml of 4,4'-diaminodiphenyl ether. The phase contains about 2 mg / ml of p-aminophenol, 15 mg / ml of 4,4'-diaminodiphenyl ether and a small amount of other impurities.

The results are summarized in the following table.

Claims (1)

Para-amino phenol is prepared by catalytic reduction of nitrobenzene in an acid medium, and an aqueous phase containing mainly para-aminophenol is extracted by selective extraction of an impurity 4,4′-diamino diphenyl ether with an organic solvent. And an organic aniline-toluene phase containing para-aminophenol, 4,4′-diaminodimethyl ether and other minor amine by-products, and then separating the aqueous phase from the organic phase to recover the para-aminophenol and extract In the process, the aqueous solution containing 4,4′-diaminodiphenylether and other small amounts of amine by-products with para-aminophenol and impurities is neutralized with a base to adjust the pH of the solution to 4.0 to 5.0 and produced. The raw aqueous solution was added as an organic solvent composed of a mixture of aniline and toluene in a ratio of 4 to 1 volume to 1 volume: 4 volume parts of aniline and toluene. Characterized in that the number of the aminophenol-hanhu the purity is increased para.